Rutba Office 2.24: the Locker, folders encrypted file by file where they already are

Many ways of encrypting a folder ask you to move it into something else, such as one large vault file. The Locker, new in Rutba Office 2.24, leaves the files where they are and encrypts each one in place. A folder on a cloud drive stays on that cloud drive, and what the drive holds is encrypted.

How a folder is locked

• File by file. Add a folder and its files are locked in place. Each becomes its own encrypted file beside the others, with its name shown or hidden as you choose.
• Large files in pieces. A file over 50 MB is kept in pieces, so a cloud drive uploads only the parts that changed.
• You decide what is locked. New files in a locked folder are listed as not locked until you lock them. Lock or unlock one file, a subfolder or all of them. An unlocked file is an ordinary file in the same place.
• Rules. A list of patterns in a folder says which files to lock, such as only *.pdf.
• Earlier versions. A folder can keep up to three earlier versions of each file.

Opening it, and working on a file

Your password opens a folder on any computer, and the recovery key stands in for it if you forget. Windows Hello, by PIN, fingerprint or face, opens it on the computer where you set that up. Changing the password leaves Windows Hello and the recovery key working.

Open a file from the Locker and a temporary copy opens beside it, hidden. What you save is locked again and the copy is removed. A locked file does not open by double-clicking it in File Explorer, so the Locker is the way in.

When it locks by itself

It locks after the idle time you set, on Lock now, when the computer sleeps or the screen locks, when Office quits, and when you close the Locker window. Clicking or typing in the Locker counts as use.

The idle lock and closing the window both wait while a document from the Locker is open in an Office window. Any other lock removes the temporary copy from the disk and leaves that document open in its window, where it can still be read. Save still works there. What you save waits unlocked and hidden, and is locked in when you next unlock.

Whatever is in that hidden folder at the next unlock becomes the file’s new version, and the Locker does not check which program wrote it. The version before it is kept with the earlier versions, if the folder keeps them. To keep both, use Save as with a new name in the locked folder.

Sending one file to someone

Send to someone locks a copy with a password of its own. Attach it to an email in Mail, or save it and send it any way you like. The other person presses Open a sent file in their Locker and needs no locker password of their own. Give them the password a different way from the file. A sent file’s name shows on the file and in the email, and only its contents are locked.

The cryptography and the file format

The encryption is AES-256-GCM, with keys from scrypt and HKDF-SHA256, all from the standard crypto library that ships inside the app. Every locked file, folder key file and keyring has its format version written in it, and the format is published in the repository for anyone to read.

Files locked with this version will open in every later one. A file made by a newer Rutba Office is reported as needing an update and is left untouched.

Known limits of this first version

• It has not had an outside security review.
• Its screens are in English only for now.
• Windows Hello is available on Windows only, and only if a PIN or similar is set up there. Resetting the Windows PIN can remove the Locker’s key. You then unlock with the password and turn Windows Hello on again.
• Removing a plain file overwrites it first, but an SSD or a cloud drive’s history can still hold old copies. Lock a folder before you sync it.
• Deleting a file in the Locker removes its earlier versions too, and cannot be undone.

Also in 2.24

Mail drafts had a real fault. Clicking from one draft to another left the first draft’s words in the form, where Save or Send could put them under the second draft’s recipients. Each draft now shows its own words, and one you changed is kept in Drafts when you click away. Turning the AI tools off and on again while an AI app is connected no longer shuts that app out of Mail, Calendar, Contacts and databases until it is restarted.